1. Field of the Invention
This invention pertains generally to signal apparatus and, more particularly, to signal apparatus, such as a light emitting diode (LED) display circuit employing a number of LEDs. The invention also relates to LED drive circuits. The invention further relates to display systems including an LED display circuit and an LED drive circuit.
2. Background Information
A known problem with a “naked” LED, which is employed in a local circuit without any active drive electronics, is that induced noise on the drive signal conductor from a remote drive circuit may run the risk of causing the “naked” LED to light inadvertently, since the “naked” LED may start to light in response to relatively very low power.
The use of hardware check pulses for vitality checking of an LED drive circuit is not compatible with “naked” LEDs, since these LEDs will flash if quickly turned ON-OFF-ON or OFF-ON-OFF. In contrast, hardware check pulses do work with an incandescent light signal because such pulses do not cause an immediate light output when power is applied, but still provide a path for the drive current.
It is known to provide a reverse bias voltage directly to a light emitting element such that it does not cause light emission. See, for example, U.S. Patent Application Publication No. 2006/0022900.
There is room for improvement in signal apparatus, such as light emitting diode (LED) display circuits. There is also room for improvement in LED drive circuits. There is further room for improvement in display systems including an LED display circuit and an LED drive circuit.